The hydraulic brake system must be bled any time one of the lines is disconnected or any time air enters the system. If the brake pedal feels spongy upon application, and goes almost to the floor but regains height when pumped, air has entered the system. It must be bled out. Check for leaks that would have allowed the entry of air and repair them before bleeding the system. If air was introduced at the master cylinder (reservoir level dropped too low or fittings were disconnected), then bleeding must begin at the master cylinder assembly. Some cylinders are equipped with bleeder screws, while others must be bled through the fittings (by loosening and tightening them while the brake pedal is depressed). Once the master cylinder is purged of air, the wheel points should be bled in the correct sequence: right rear wheel cylinder, left rear, right front, and left front.
See Figures 1, 2 and 3
This method of bleeding requires two people, one to depress the brake pedal and the other to open the bleeder screws.
- Clean the top of the master cylinder, remove the cover and fill the reservoirs with clean fluid. To prevent squirting fluid, replace the cover.
On cars with front disc brakes, it will be necessary to hold in the metering valve pin during the bleeding procedure. The metering valve is located beneath the master cylinder and the pin is situated under the rubber boot on the end of the valve housing. This may be taped in or held by an assistant.
- Fill the master cylinder with brake fluid.
- Install a box-end wrench on the bleeder screw on the right rear wheel.
- Attach a length of small diameter, clean vinyl tubing to the bleeder screw. Submerge the other end of the rubber tubing in a glass jar partially filled with clean brake fluid. Make sure the rubber tube fits on the bleeder screw snugly or you may be squirted with brake fluid when the bleeder screw is opened.
- Have your friend slowly depress the brake pedal. As this is done, open the bleeder screw half a turn and allow the fluid to run through the tube. Close the bleeder screw, then return the brake pedal to its fully released position.
- Repeat this procedure until no bubbles appear in the jar. Refill the master cylinder.
- Repeat this procedure on the left rear, right front, and left front wheels, in that order. Periodically refill the master cylinder so it does not run dry.
- If the brake warning light is on, depress the brake pedal firmly. If there is no air in the system, the light will go out.